A multistream radiative transfer model was used to calculate the
geographic distribution of the UV-A and UV-B dose rates at the surface of
the Earth. It used a multiyear climatology that included the effects of
ozone, clouds, surface pressure, surface albedo, temperature, and
aerosols. The results indicated that the most important factor in
determining the dose is the Suns position. Clouds reduce the dose
from a few percent under clear-sky conditions to 45% where midlatitude
depressions occur frequently.

An analysis of atmospheric concentrations of ozone-depleting halogen
species showed a decline since 1994 across a large number of chemicals led
by the decline of trichloroethane, a cleaning solvent. Its decline has now
peaked. Any future declines in emissions of ozone-depleting compounds will
have to come from limitations on emissions of other chemicals, notably
Halon-1211 (CBrClF2), whose atmospheric concentration has remained
constant and is retarding the overall decline of ozone-depleting halogens.